210 NEW UNIONIDiE OF THE 



My cabinet and cabinet of Smithsonian Institution. 

 Diam. -7 Length 1-2, Breadth 2-3 inches. 



Shell smooth, broadly elliptical, compressed, biangular and compressed behind, 

 rounded before, very inequilateral ; beaks a little prominent ; ligament rather long, 

 thin and dark brown ; epidermis dark brown, somewhat shining towards the beaks, 

 without rays, with rather close lines of growth ; umbonial slope very slightly 

 raised and rounded ; posterior slope very narrow-elliptical, compressed, carinate, 

 with two slightly raised lines from the beaks to the margin ; cardinal teeth very 

 small, striate and crenulate, disposed to be double in both valves; lateral teeth 

 very long and somewhat curved; anterior cicatrices distinct, rather small and 

 moderately well impressed ; posterior cicatrices confluent and but slightly im- 

 pressed ; dorsal cicatrices small, and placed nearly in the centre of the cavity of 

 the beaks ; cavity of the shell very shallow and wide ; cavity of the beaks very 

 shallow ; nacre purple and very iridescent. 



Remarks. — This species belongs to the group of which complanatus is the type. 

 There are three specimens before me of different ages— the largest 2-7 inches 

 wide. In outline it is very nearly the same as viridiradiatus, (nobis,) and like it 

 the greater diameter is nearly in the middle of the disks, making it somewhat lenti- 

 cular. It is, however, higher in the posterior slope and more carinate, and the 

 color of the epidermis is totally different, and it is also destitute of rays. I name 

 it after Dr. Mercer, who sent it, with many other species from Georgia, to the 

 Smithsonian Institution. 



Margaritana quadrata. PI. 32, fig. 279. 



Testa lsevi, oblonga, subcompressa, ad latere planulata, subsequilaterali, postice obtuse" angulata, antice 

 rotund^; valvulis subtenuibus, antice paulisper crassioribus ; natibus prommulis, ad apices un- 

 dulatis ; epidernride luteol&, viridi-radiata ; dentibus cardinalibus subgrandibus, obliquis, compressis, 

 triangularis erectis subcurvisque ; margarita alba, superne salmonis colore tinct&, valde iridescente. 



Shell smooth, oblong, somewhat compressed, flattened at the side, nearly equi- 

 lateral, obtusely angular behind, round before ; valves rather thin, slightly thicker 

 before ; beaks slightly prominent, undulate at the tips ; epidermis yellowish, with 

 green rays; cardinal teeth rather large, oblique, compressed, triangular, erect 

 and somewhat curved; nacre white, tinted with salmon color above and very 



iridescent. 



Proe. Acad. Nat. Sci., 1861, p. 41. 



Hah. — East Tennessee, President Estabrook. 



My cabinet. 

 Diam. -5, Length 1, Breadth 1-5 inches. 



Shell smooth, oblong, somewhat compressed, flattened at the side, nearly equi- 

 lateral, obtusely angular behind, round before ; substance of the shell rather thin, 



